Showing papers by "John M. Blondin published in 1997"

X‐Rays from the Impact of SN 1987A with Its Circumstellar Ring

Abstract: We present models for the hydrodynamics of the impact of the envelope of SN 1987A with its inner circumstellar ring and for the resulting X-ray spectra and light curves. If the impact begins in A.D. 2000, the X-rays should be bright enough to resolve several emission lines with spectrometers on-board AXAF and Astro-E; if it begins in A.D. 2005, the X-rays will be roughly an order of magnitude brighter and have harder spectra. We compare our results with those from previous models and provide scaling laws to extend our results to models with impact times and ring densities different from those presented here. Within a few years after impact, the X-rays will brighten and their spectra will harden, owing to a complex variation of temperature within the shocked ring caused by the merger of primary and reflected shocks. The impact will continue for decades, and the X-rays will steadily increase in luminosity and temperature as the shock enters heretofore unseen matter in the ring.

The Interplay Between Protoneutron Star Convection and Neutrino Transport in Core Collapse Supernovae

Abstract: We couple two-dimensional hydrodynamics to realistic one-dimensional multigroup flux-limited diffusion neutrino transport to investigate protoneutron star convection in core collapse supernovae, and more specifically, the interplay between its development and neutrino transport, for both 15 and 25 solar mass models. In the presence of neutrino transport, protoneutron star convection velocities are too small relative to bulk inflow velocities to result in any significant convective transport of entropy and leptons. A simple analytical model supports our numerical results, indicating that the inclusion of neutrino transport reduces the entropy-driven (lepton-driven) convection growth rates and asymptotic velocities by a factor of 3 (50) at the neutrinosphere and a factor 250 (1000) at a density of 10^{12} g/cm^{3}, for both our 15 and 25 solar mass models. Moreover, when transport is included, the initial postbounce entropy gradient is smoothed out by neutrino diffusion, whereas the initial lepton gradient is maintained by electron capture and neutrino escape near the neutrinosphere. Despite the maintenance of the lepton gradient, protoneutron star convection does not develop over the 100 ms duration typical of all our simulations, except in the instance where ``low-test'' initial conditions are used, which are generated by core collapse and bounce simulations that neglect neutrino-electron scattering and ion-ion screening corrections to neutrino- nucleus elastic scattering.

Collimation of Astrophysical Jets: The Proto-Planetary Nebula He 3-1475

Abstract: The proto-planetary nebula He 3-1475 was imaged in the [N II] λ6584 line with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. This image has revealed what appear to be large-scale flows being collimated into narrow bipolar jets. This is a unique object: we may be observing the actual collimation process of an astrophysical jet. Analytical models and hydrodynamical simulations suggest that the jet in He 3-1475 may be produced by purely hydrodynamical means, through focusing of a weakly collimated bipolar outflow into jets by oblique radiative shocks.

X-Ray and Ultraviolet Line Emission from SNR 1987A

Abstract: The soft X-ray emission seen from SN 1987A and the apparent deceleration of the radio source expansion suggest that the supernova blast wave has encountered a moderately dense H II region interior to the inner circumstellar ring We simulate the hydrodynamics of this interaction and calculate the resulting X-ray and ultraviolet emission-line spectrum and light curves The soft X-ray spectrum is dominated by emission lines of hydrogenic and helium-like C, N, O, and Ne; it is consistent with the ROSAT observations if Fe is depleted on grains N V λλ1240 emission should be observable easily with the Hubble Space Telescope The blast wave should strike the inner circumstellar ring around AD 2007

Hydrodynamical Models of Line-driven Accretion Disk Winds

Abstract: We present here one-dimensional analytic hydrodynamic models and both one-dimensional and two-dimensional numerical hydrodynamic models for line-driven accretion disk winds from cataclysmic variable (CV) systems. Using the one-dimensional analytic models we explore the physical conditions necessary for the existence of a disk wind and study the dependence of wind speed and mass-loss rate on radius. The results of our two-dimensional model are consistent with the spectrum observed from CVs in the polar nature of the wind, the maximum absorption at roughly half the terminal speed of the P Cygni profiles, and the order of magnitude of the terminal speeds. For disk luminosity Ldisk = L☉, white dwarf mass Mwd = 0.6 M☉, disk radius Rdisk = R☉, and sound speed a = 10 km s-1 we obtain a wind mass-loss rate of wind=2 × 10−14 M yr-1 and a terminal velocity of ~3000 km s-1. The two-dimensional models show that centrifugal forces produce shocks in the disk wind. If these shocks were absent, the mass-loss rates obtained would be too low to produce the optical depths required to explain the P Cygni profile of CVs. The two-dimensional models demonstrate the importance of centrifugal forces in winds from accretion disks and thus the necessity of models where these forces may be represented.

3-D Hydro dynamic Simulation of Accretion Disk Formation in LMC-X4

Abstract: We present preliminary results of a time-dependent, three-dimensional hydrodynamic simulation of LMC-X4, an HMXB known to be undergoing RLOF. The simulation is initialized with the collapsed companion embedded in the undisturbed primary wind. The primary is in contact with the Roche surface, although no tidal stream or accretion disk is initialed; they are allowed to form independently. Several features of general interest to disk-fed HMXBs are apparent in the simulation. First, the primary immediately develops a compressed-wind disk in the orbital plane. This may be a natural result in most disk-fed HMXBs. Fora circularized system in an orbit close enough for RLOF to take place, we may expect the primary to be in corotation. The surface velocity may then be a significant fraction of the breakup velocity, leading to a compressed-wind disk.

Hydrodynamical Models of Line-Driven Accretion Disk Winds

Abstract: The existence of winds from cataclysmic variables (CVs) has been known for some time, there are a variety of unresolved questions surrounding this phenomenon. These include: the origin of the apparent polar nature of the winds; the rate of mass loss in the winds and the associated driving mechanism; the origin for the characteristic shapes of the UV resonance line profiles, particularly the absorption component; and the apparent association between outburst state and the wind existence. Resolution of all these issues depends on understanding the dynamics of the wind. In this paper we describe one and two dimensional models for disk wind dynamics. Using 1D analytic models we have explore the physical conditions necessary for the existence of a disk wind, and study the dependence of wind speed and mass loss rate on radius. This leads to a criterion which must be satisfied by the rate of increase in the radiation field with height above the disk surface and by the parameters describing the line radiation pressure force (c.f. Castor, Abbott and Klein, 1976).

Effect of Ambient Wind Velocity on Planetary Nebula Morphology

Abstract: Planetary Nebulae (PNe) are formed by the interaction of the fast wind from a post-Asymptotic Giant Branch Star with the slow ambient wind from a previous epoch. If the two interacting winds have constant properties, the velocity of the PN shell tends towards a constant with time and the shape becomes self-similar. Additionally, if the velocity of the fast wind is much higher than the expansion velocity of the shell, the interior of the hot shocked bubble becomes isobaric. Using semi-analytical methods, complemented by hydrodynamic simulations, we have calculated the shapes of PNe in the self-similar stage (Dwarkadas et al. 1996). We have investigated the contribution of the ambient wind velocity to PN morphology, which has hitherto not received much attention since the work of Kahn & West (1985). We find that the nebular morphology is a consequence of the density contrast between pole and equator in the ambient medium, the steepness of the density profile and the velocity of the ambient wind; classification of PNe purely on the basis of the first two factors may be misleading. In particular, the ratio of ambient wind velocity to PN velocity is important in determining whether the nebula shows a bulge or a cusp at the equator. A high density contrast coupled with a low velocity for the external medium gives rise to extremely bipolar nebulae. For large density contrasts and a significant value of the slow wind velocity, the surface density maximum of the shell shifts away from the equator, giving rise to peanut-shaped structures with pronounced equatorial bulges. As long as the external wind velocity is small compared to the expansion velocity of the nebula, the PNe tend to be more bipolar, even with a moderate density contrast. If the PN velocity is close to that of the external wind, the shape is relatively spherical. However, inclusion of an asymmetric velocity profile in the slow wind, with the velocity increasing towards the pole, can lead to a bipolar nebula if the equatorial velocity is sufficiently low. Preliminary results with a slow wind velocity increasing towards the equator (as is found in calculations of common envelope evolution) show that the nebulae tend to be more oblate, which is not often observed in nature. Representative results for shapes of PNe using various values of the relevant parameters are presented.